Microwave heating apparatus



United States Patent 3,427,422 MICROWAVE HEATING APPARATUS Paul CurtMiiller, Wettingen, Aargan, Switzerland, assignor to PatelholdPatentverwertungs- & Elektro- Holding AG., Glarus, Switzerland Filed May18, 1966, Ser. No. 551,106 Claims priority, application Switzerland, May19, 1965,

6,988/ 65 US. Cl. 219-1055 Int. Cl. H05b 9/00, 9/06, 5/00 5 ClaimsABSTRACT OF THE DISCLOSURE The present invention relates to microwavehigh frequency heating apparatus of the general type including amicrowave generator with means to apply a microwave energy beam unto thematerial or substance to be heated disposed in an enclosed heating spaceor chamber, and more particularly to improved heating apparatus of thistype for the heating of easily coagulable liquid substances, and/orsubstances liable to bubble or foam formation during heating, inparticular preserved blood, and stored in non-metallic bottles or thelike containers.

Among the objects of the invention is the provision of high frequencyheating apparatus of the referred to type by which a liquid, such asblood plasma, can be heated to a desired temperature substantiallyinstantly and relatively rapidly without the danger of coagulation orfoam formation; whereby the desired final heating temperature ismaintained within relatively close tolerances; which apparatus is bothsimple in design and efficient in operation; and which may be fabricatedeconomically and used at low operating cost.

The invention, both as to the foregoing and ancillary objects as well asnovel aspects thereof, will be better understood from the followingdetailed description of a preferred practical embodiment, taken inconjunction with the accompanying drawing forming part of thisspecification. In the drawing, wherein like reference numerals denotelike parts of the different views thereof:

FIG. 1 shows, in part diagrammatically and in part in section, microwaveheating apparatus constructed in accordance with the principles of theinvention;

FIG. 2 shows a section, to an enlarged scale, taken on line 22 of FIG.1; and

FIG. 3 more clearly shows the temperature sensing device of theautomatic temperature control forming part of the preceding figures.

With the foregoing objects in view, the invention, according to one ofits aspects, involves generally the provision of means providing anenclosed microwave treating space or chamber having disposed therein anopenended hollow and rotatably mounted container holder of microwavepermeable insulating material, the inside space enclosed by said holdersubstantially conforming to the configuration of the containers storingthe liquid to be heated, in particular preserved blood or a like easilycoagulable liquid substance. There is furthermore provided according tothe invention means to frictionally support the containers by or urgethe same against the inside wall of the holder, to cause rotation of thecon- 3,427,422 Patented Feb. 11, 1969 tainers and the liquid storedtherein together with the holder and to effect a close thermal contactwith the temperature-sensing element of an automatic temperature controldevice operably combined with the heating apparatus of the invention, inthe manner described in further detail in the following.

In operation, the container holder is rotated about an axis coincidentwith the axis of the container mounted therein, such as a bottle or thelike oblong storage vessel, while a microwave energy beam is impingedfrom a microwave generator (magnetron, klystron, etc.) upon the holderand the liquid container via suitable wave guide means connecting thegenerator with the heating space or chamber. The temperature-sensingelement in cooperation with the automatic temperature control deviceserves to heat the liquid by direct action of the microwave energy to adesired temperature and to maintain it at this temperature, for example35 in the case of blood plasma. Due to the rotation of the liquid,coagulation and bubble or foam formation is substantially eliminated orminimized and the heating time to the desired temperature reduced to aminimum.

According to an especially advantageous construction of the heatingapparatus according to the invention, the oblong bottles or the likecontainers, and in turn the rotatable container holder, are disposed atan inclined angle with the microwave beam being impinged thereon in asubstantially upward or vertical direction, in such a manner as toachieve an improved mixing or stirring effect (by friction with thebottle wall) on the liquid stored in the bottle or container, combined'with ease in handling and exchange of the containers. Besides, theinclination of the containers and application of the microwave energy atan angle or vertically in relation to the rotating axis of the liquidresults in a relatively faster heating of the lower portion of theliquid, causing this warmer liquid to rise to the top with the result ofa greater mixing or stirring action and, in a turn, a further reducedheating time. The apparatus of the invention has been found especiallysuitable for the heating of preserved blood in substantially preventingcoagulation or foam formation, while reducing heating time to a minimum.

Further details and features of the invention will become more apparentas the description proceeds in reference to the drawing.

The microwave treating space proper or chamber 10 is closed by a hingedsnap lid or cover 11 for the positioning therein and withdrawal of thecontainers storing the liquid to be heated. Rotatively mounted in aninclined wall 12 of the chamber 10, by means of a bearing 13, is acontainer or vessel holder 14 in the form of an open-ended hollow memberconsisting of microwave permeable insulating material and having aninside space substantially conforming to the configuration of a bottleor the like container 20 storing the liquid to be heated, such aspreserved blood or plasma. As a consequence, the holder 14 and with itthe container 20, being driven by an electric motor 15 via a reductiongearing 16, 17 and friction coupling 18, is rotated, as indicated by thearrow a' in the drawing, about an inclined axis enclosing a suitableangle with the horizontal of preferably less than 45 As an example, arotating speed of the container of about 30 revolutions per minute andan incline angle of about 30 have been found to produce satisfactoryresults in treating or heating blood plasma.

The container 20, which can be easily inserted into and withdrawn fromthe holder 14 on account of the inclined mounting of the latter, is heldor retained in the holder by friction, whereby to rotate together withsaid holder and to maintain a close thermal contact with thetemperature-sensing element mounted upon the inside wall of the holderand forming part of an automatic 3 temperature control device, serving,in cooperation with a suitable microwave generator, to raise thetemperature of the liquid to be treated to and to maintain it at adesired temperature, such as 35 in the case of preserved blood.

In the example shown, the friction mounting means for the container iscomprised of a rubber or the like flexible sleeve 21 encircling thehollow portion of the holder 14 in stretched condition, said sleeveacting upon the outer perimeter of the container 20 via a pair (in theexample shown) of non-metallic pressure pins 22 of greater length thanthe wall thickness of said holder and mounted slidably in radial boresof said holder, whereby said pins fitted with suitable outer headsengage the inside of the sleeve 21, on the one hand, and the container,on the other hand, to result in an adequate frictional engagementbetween the container 20 and holder 14, or temperature-sensing devicedescribed in the following.

The temperature-sensing device comprises, in the example shown, a thinmetallic sheet 23 having soldered or otherwise connected thereto athin-walled metal casing or screen 23 disposed in a recess of the holder14 and housing a pair of temperature-sensitive resistors or thermistors25 and 26 supported in heat-conducting contact by the sheet 23. As anexample, the element 23 may consist of a thin bronze sheet having athickness of from 0.1 to 0.3 millimeter, though not limited thereto, andpossessing a very small heat capacity. The thermistors 25 and 26 beingelectrically and magnetically shielded by the housing 23 are connected,via suitable conductors (not shown) mounted in shielded condition withinthe axis of the holder 14, each to a pair of slip rings 29, 30,respectively, cooperating in a known manner with pairs of stationarybrushes or sliding contacts 27, 29, respectively, the latter being inturn connected to an automatic temperature control device 39 of knownconstruction connected to the power supply 40 of the microwave generator36 of the heating apparatus, such as a magnetron, klystron, etc., havingits output applied, via a suitable coupling wave guide 37, to theheating chamber 10, to impinge a microwave energy beam upon the liquidin the container 20 to be heated. The outlet end of the wave guide 37may be closed in water-tight fashion by a Teflon or the like microwavepermeable plate or closure 38.

In order to prevent operation of the heating apparatus during idlingcondition, that is, when no container is placed in the holder 14, orduring exchange of the containers, a safety switch 31 operated by aspring-urged plunger 32, mounted axially within the holder 14 and sliprings 29, and engaged at its inner end by the bottom of the container 20in the mounted position, serves to disconnect the generator as long asthere is no container in the device. Similarly, the generator 36 may bedisconnected during opening of the lid 11 by the provision of a furthersafety switch 33 operably connected with said lid, as indicated.

In operation, the temperature control device 39, including a suitabletemperature standard, operates in a known manner to connect anddisconnect the generator 36, via its power supply 40 in the exampleshown, whenever the temperature of the container or liquid storedtherein falls below or rises above the desired value, that is 35 on thecase of preserved blood, whereby to raise the liquid to and toautomatically maintain it at said temperature within a desired accuracyor tolerance range.

In order to prevent temperature fluctuations of the heating apparatusduring prolonged use in the operating room or the like, the chamber 10and generator 36 are enclosed, according to an improved feature of theinvention, in an outer housing 35 having its temperature stabilized ormaintained at the temperature of the ambient atmosphere. For thispurpose, the microwave generator 36 together with the coupling waveguide 37 are suction cooled by the provision of a fan or blower 41disposed in airtight manner between the outlet duct of the generatorcooling device and an opening in the housing wall 35, the inlet of thegenerator cooling device being connected with the outside atmospherethrough suitable inlet ports in the housing wall 35. As a consequence,air is continuously sucked into the housing and forced through thegenerator cooling ducts, as indicated by the arrows b, c and d in thedrawing, the heated air being discharged to the outside, in such amanner as to maintain the temperature within the housing 35 within arange of 12 of the ambient temperature and to maintain the liquidtemperature within i1 of 35 C. in the case of preserved blood as anexample. After the temperature, upon initially starting the device, hasreached the desired value, a control signal by the sending resistor 25applied via the contacts 37 causes the automatic control to disconnectthe generator 36, and vice versa, to reconnect the same after thetemperature decreases below said value to a predetermined extent, in amanner well known in the operation of automatic temperature controldevices.

The second thermistor, 26 connected to the contacts 29 is independent ofthe thermistor 25 and may serve to operate a suitable temperatureindicator or measuring device (not shown).

With specific reference to the heating of preserved blood, the microwavepower is advantageously adjusted such that a container of 500 cm.capacity may be heated from +5 to +35 C. in approximately 3 to 5minutes. The degree of accuracy is within 1 C. even with contents offrom 300 to 500 cm. This accuracy and the relative short heating timecan be attained only if the blood is moved slowly and gently, inparticular by rotation, as shown and described, to avoid the formationof bubbles. It is, however, also possible to employ, in place ofcontinuous rotation, a to and fro or rocking motion of the holder orcontainer mounted therein. In the latter case, the containers may bedisposed in horizontal, inclined or vertical position.

Besides, the diffused irradiation of the blood or other liquid in thecontainer 20, disposed at an incline angle of less than 45, in theexample shown and described in the foregoing, largely prevents the bloodfrom coagulating.

In the foregoing the invention has been described in reference to aspecific illustrative device. It will be evident, however, thatvariations and modifications, as well as the substitution of equivalentparts or devices for those shown for illustration, may be made withoutdeparting from the broader scope and spirit of the invention as setforth in the appended claims. The specification and drawings areaccordingly to be regarded in an illustrative rather than in arestrictive sense.

I claim:

1. Microwave heating apparatus for the treatment of liquids stored innon-metallic containers comprising in combination:

( 1) means to provide an enclosed microwave treating space,

(2) an oblong open-ended hollow container holder 9f microwave-permeableinsulating material enclosing a space substantially conforming to theconfiguration of the containers of the liquid to be heated, forremovably mounting a container within said holder,

(3) resilient means to effect frictional engagement between said holderand the container mounted therein,

(4) means rotatively supporting said holder within said treating spaceabout its axis forming a predetermined vertical incline angle with thehorizontal,

(5) means to rotate said holder and container mounted therein about saidaxis,

(6) a microwave generator including wave guide coupling means connectingthe same with said treating space, to impinge a microwave beam in asubstantially vertically upward direction unto said holder and thecontainer mounted therein,

(7) temperature-sensing means upon said holder in thermal contact withthe container mounted therein, and

(8) automatic temperature control means operably connecting said sensingmeans with said generator, to heat the liquid stored in said containerto and maintain it at a predetermined temperature.

2. Microwave heating apparatus as claimed in claim 1, saidtemperature-sensing means consisting of a strip of heat-conducting metalof low thermal capacity and mounted upon the inside wall of said holder,said strip held in close thermal contact with the container mountedtherein by said resilient means, and a heat-sensitive electricalresistor disposed in a recess of said holder and afiixed to said strip.

3. Microwave heating apparatus as claimed in claim 2, including metallicscreening means enclosing said resistor.

4. Microwave heating apparatus as claimed in claim 1, said resilientmeans consisting of a sleeve of flexible material encircling said holderin stretched condition, and at least one pressure pin of greater lengththan the wall thickness of said holder, said pin arranged slidablewithin a bore through said holder with one end thereof engaging saidsleeve and with its opposite end engaging the container mounted in saidholder.

5. Microwave heating apparatus as claimed in claim 1, including ahousing having air inlet and outlet means and enclosing said treatingspace, said holder rotating means,

said generator and said temperature control means, and further means toaspirate and circulate ambient air through said generator via said inletand said outlet means.

References Cited UNITED STATES PATENTS 3,081,392 3/1963 Warner 21910.553,127,495 3/1964 Polries et al. 21910.53 3,154,663 10/1964 Halvorsen2l910.49 3,177,335 4/1965 Fitzmayer et a1. 21910.55 3,185,809 5/1965Bohm et al 21910.55 3,281,568 10/1966 Haagensen 21910.55 3,315,6814/1967 Poppendiek 21910.65X

FOREIGN PATENTS 1,249,130 11/ 1960 France.

OTHER REFERENCES Mikrowellen, German Application No. 1,132,267

printed June 28, 1962 (Ke21h36) 2 pages spec., 1 sheet draw.

RICHARD M. WOOD, Primary Examiner.

25 L. H. BENDER, Assistant Examiner.

US. Cl. X.R. 2l9--10.65

